This invention relates generally to mass spectrometers and methods of their use and more specifically to mass spectrometers used for screening samples and methods of screening samples using mass spectrometers.
Often it is important to know if a component is present in a sample. Analysts may look for one or more components of interest that may only be present in trace amounts. One way of finding out if a component of interest is present in a sample is to analyse a sample using a liquid chromatography instrument coupled with a mass spectrometer (LCMS). The properties of the component of interest may then be searched against the corresponding properties of the ions detected by the spectrometer. For example, one may search the mass spectral data for candidate ions that have a retention time, mass and potentially fragment ion mass(es) that match the same properties of the ions of interest.
Each property is searched within a tolerance window. From one aspect it is desirable to set the tolerance window relatively wide so as not to exclude candidate ions that match the ions of interest. This is necessary because the value of an experimentally determined property may deviate from its true value due to experimental conditions. However, setting the tolerance window relatively wide also increases the likelihood of a large number of false positives being detected. From another aspect, it is desirable to set the tolerance window being relatively narrow, so as to avoid detecting false positives. A compromise must therefore be made when setting the width of each tolerance window, which may result in an increased likelihood of false positives and/or false negatives being detected.
Therefore, it is desired to provide a screening method which screens for known compounds, whilst reducing the number of false positives and false negatives that are detected.